1. Field Of The Invention
This invention relates to control circuitry, and more particularly, to apparatus for limiting an output voltage range provided by power supplies which furnish an undesirably wide range of voltages.
2. History Of The Prior Art
Portable computers are a rapidly growing segment of the personal computer market. The portable computer market has taken longer to develop because of the inability of manufacturers to produce such computers which are capable of operating for long enough periods on a single battery charge to make them useful. Initially, portable computers were constructed using the same components as desktop computers and adding a battery to power the components. These computers were quite heavy and would operate for little over an hour on batteries. Then, attempts were made and continue to make batteries more powerful and lighter so that they will operate computers for longer periods. In general, newer types of batteries are lighter and more powerful than older types. However, at the same time, other attempts have proceeded to reduce the power requirements of portable computers by utilizing components which are lighter or which require less power so that computers can operate for longer periods using batteries which are available.
The attempts to reduce the power requirements of portable computers have produced circuits which function at different voltage levels. Some times these levels vary within a computer. Certain circuitry may operate at a first voltage of, for example, three and one-half volts; while other circuitry operates at a second voltage level such as five volts. In other instances, all of the circuits of one computer use a supply voltage of three ad one-half volts, while those of another computer use a power supply of five volts.
This use by computer manufacturers of different supply voltages creates a number of problems for those who manufacture components which are used with portable computers. A major problem is that it is necessary to manufacture different components for each section of the market which has different source voltage requirements. Some of these market sections may be too small to warrant the cost involved in producing a particular component. Other market sections may require that two devices be used in the same computer.
Consequently, it would be desirable to furnish some arrangement which would allow peripheral components to function with different sources of voltage so that different components need not be designed for the different segments of the market which use different source voltages.